In recent years, foam materials have been attracting attention in view of achieving lightweight. However, if a composition containing a resin or elastomer is merely foamed, the mechanical strength will decrease, causing problems such as deterioration and deformation after long-term use. For this reason, such a composition is made into a crosslinked foam, thereby finding a wide range of applications as a material that is lightweight and has a high mechanical strength, such as automobile-related parts, construction-related parts, various packaging materials, and daily necessities.
Ethylene-vinyl acetate copolymers (EVA) are known as representative crosslinked foams; however, because EVA has a low melt tension, defoaming easily occurs, preventing the expansion ratio from increasing, resulting in an increased specific gravity. Furthermore, another problem thereof is that the defoaming causes significantly rough skin.
Thus, proposals have been made regarding crosslinked foams using ethylene-α-olefin-based copolymers. Patent Document 1 discloses a crosslinked foam obtained by crosslinking and foaming an ethylene-α-olefin-based copolymer, using an organic peroxide, a crosslinking coagent, and a foaming agent. Patent Document 2 discloses a crosslinked foam obtained by crosslinking and foaming a composition obtained by adding EVA and/or low density polyethylene to an ethylene-α-olefin-based copolymer. Furthermore, studies have been conducted on modifying the properties and improving the physical properties of a crosslinked foam by adding a styrene-based block copolymer to an ethylene-based copolymer. Patent Document 3 discloses a crosslinked foam obtained by adding a specific proportion of a styrene-based block copolymer to an ethylene-based copolymer.    Patent Document 1: Japanese Patent Laid-Open No. 2000-344924    Patent Document 2: Japanese Patent Laid-Open No. 2002-302565    Patent Document 3: Japanese Patent Laid-Open No. 2004-107519